The concept of a pneumatic tire with puncture sealing properties is old and many attempts to obtain a satisfactory puncture sealing pneumatic tire have been made. Historically such attempts have entailed modifying pneumatic tires in such a way so as to retard or prevent a loss of air and consequential deflation of the tire after being punctured with a sharp object, such as a nail.
Examples of such teachings date back to the early 1900's wherein relatively simple disclosures were made to provide a tire with a strip of unvulcanized rubber which, it is stated, would have puncture sealing properties. More recent teachings relate to more sophisticated tire constructions, sealant compositions and methods wherein a sealant material is encased or encapsulated in between calendered layers (see U.S. Pat. Nos. 3,048,509, and 4,228,839).
Many additional methods, sealants and tire constructions have been suggested for puncture sealant pneumatic tires. However, all of these ideas have had certain drawbacks. For example, the use of fluid puncture sealant coatings which seal by flowing into the puncture hole has sometimes been unsuccessful primarily because sealant coatings may flow excessively and thus tend to cause the tire to become out of balance. Also, many times such a sealant coating is not operable or effective over a wide temperature range extending from summer to winter conditions. Central cores of cellular material which will physically maintain the shape of the tire when punctured can place a restriction on the maximum speed of a vehicle on which they are used because of potential breakdown or destruction of the cells caused by the effects of heat and distortion. More complicated structures wherein the sealant material is encased in a vulcanized material are usually expensive to manufacture and can also create balance and suspension problems due to the additional weight required in the tire.
Puncture sealing tires have been built wherein a layer of degraded rubber which is tacky or gummy (of low viscosity) is assembled into the unvulcanized tire. This method of construction is usually only reasonably possible when the degraded layer of rubber is laminated with another ungraded layer which permits its handling during the tire building procedure. This is because the tacky, sticky nature and lack of strength in degraded rubber make it very difficult to handle alone without additional support and a barrier to keep it from sticking to a tire building machine or curing apparatus. By laminating the degraded rubber layer between two or more undegraded rubber layers it is capable of retaining its structural integrity during the vulcanization operation wherein high pressures are applied to the tire which would displace the degraded rubber layer from its desired location if not laminated. Such a lamination procedure adds greatly to the cost of building a tire. Thus, such a lamination procedure has not been widely accepted on a commercial basis for building puncture sealing pneumatic tires. There has been a continuing desire for a pneumatic tire having an effective puncture sealing feature and for a simple and practical method of preparing such a tire.
This invention provides a method for building a tire with puncture sealing features by degrading a built-in rubber layer (polymer composition) in a special manner during the vulcanization of the tire. Therefore, during the tire building procedure the polymer composition layer (which will be the sealant layer after the tire is cured) is of high viscosity and can be easily handled.